JP4905060B2 - Reception device and data reproduction method - Google Patents

Description

  The present invention relates to a receiving apparatus and a data reproducing method for reproducing video / audio data transmitted from a transmitting apparatus via a network in real time, and in particular, to reduce the influence of jitter in network transmission and to reproduce video and audio with good quality. The present invention relates to a receiving apparatus and a data reproducing method.

  When video and audio are transmitted and reproduced in real time via a network such as the Internet, in order to keep the quality of the reproduced video and audio good, a communication device on the transmission side (hereinafter referred to as “transmission device”) It is important that the communication device on the reception side (hereinafter referred to as “reception device”) operates with accurate clock synchronization.

  In order to realize clock synchronization between the transmission apparatus and the reception apparatus, a method of transmitting time information from the transmission apparatus to the reception apparatus multiplexed with video data and audio data (see, for example, Patent Document 1), A method of temporarily storing data and audio data in a buffer, and monitoring the usage status of the buffer and adjusting the clock is known (for example, see Patent Document 2).

Japanese Patent Laid-Open No. 11-308203 JP 2006-148227 A

  However, the method of transmitting time information multiplexed from video data and audio data from the transmission device to the reception device requires that the time information is transmitted at a correct time interval. When this method is used in a network with a large fluctuation (hereinafter referred to as “jitter”), there may be problems such as dropped frames of images, color shifts, extended sound and fast-forwarding.

  Also, in the method of adjusting the clock by monitoring the buffer usage, the buffer absorbs a certain amount of jitter, so the clock can be corrected more broadly than the above method, but large jitter due to communication congestion etc. When it occurred, the clock could not be corrected.

  The present invention has been made to solve the above-described problems caused by the prior art, reduces the influence of jitter in network transmission, and reproduces video and audio with good quality and data reproduction. It aims to provide a method.

  In order to solve the above-described problems and achieve the object, according to one aspect of the present invention, there is provided a receiving device that reproduces video / audio data transmitted from a transmitting device via a network in real time. Clock generating means for generating a clock for reproducing data, a buffer for temporarily storing the video / audio data, and two pieces of time information transmitted from the transmission device multiplexed with the video / audio data By calculating a time difference, a first difference calculation means for obtaining a time difference in which the two time information is transmitted in the transmitting device, a time when one of the two time information arrives at the receiving device, and the other is Second difference calculation means for calculating the time difference between the times of arrival at the receiving device, and the difference between the calculation results of the first difference calculation means and the second difference calculation means; Jitter amount acquisition means for acquiring a jitter amount in the network by subtracting a data fluctuation amount that may occur due to a clock fluctuation generated by the clock generation means from a data amount of the video / audio data transmitted at a corresponding time And a control amount correction unit that corrects a control amount applied to the clock generation unit so that a value obtained by subtracting the jitter amount acquired by the jitter amount acquisition unit from the data amount stored in the buffer is constant. It is characterized by having.

  According to another aspect of the present invention, there is provided a data reproduction method in a reception device for reproducing video / audio data transmitted from a transmission device via a network in real time, wherein the video / audio data is temporarily stored in a buffer. An accumulation step for accumulating, and calculating a time difference between two time information transmitted multiplexed with the video / audio data from the transmission device, thereby obtaining a time difference when the two time information is transmitted in the transmission device. A difference calculation step of one, a second difference calculation step of calculating a time difference between a time when one of the two pieces of time information arrives at the receiving device and a time when the other arrives at the receiving device, From the data amount of the video / audio data transmitted at a time corresponding to the difference between the calculation results of the first difference calculation step and the second difference calculation step, the video / audio data is calculated. A jitter amount acquisition step of acquiring a jitter amount in the network by subtracting a data fluctuation amount that may occur due to a fluctuation of a clock generated for reproducing the jitter, and the jitter amount acquired by the jitter amount acquisition step And a control amount correction step of correcting a control amount for changing the clock so that a value subtracted from the amount of data stored in is constant.

  According to the aspect of the present invention, the control amount correction unit subtracts the jitter amount acquired by the jitter amount acquisition unit based on the time information from the memory usage amount of the buffer for storing the video / audio data, thereby controlling the clock generation unit. Since it is configured to determine the amount, the influence of jitter in the network is reduced compared with the case where the control amount of the clock generation means is simply determined based on the memory usage, and video and video with good quality can be reduced. Audio can be played back.

  In another aspect of the present invention, in the above aspect of the invention, a data amount calculation for calculating a data amount of the video / audio data to be transmitted at a time corresponding to a calculation result of the first difference calculation means. Means, a data amount counting means for counting the data amount of the video / audio data actually transmitted while the two time information are received, and a data amount counted by the data amount counting means, When the amount of data is smaller than the amount of data calculated by the data amount calculation means, invalid data addition means for adding invalid data corresponding to the difference in data amount to the buffer, and invalidity added by the invalid data addition means It further comprises invalid data deleting means for deleting the invalid data before the data is reproduced as video / audio data.

  According to the aspect of the present invention, the amount of data calculated from the received time information is compared with the amount of actually received data. If the amount of actually received data is small, a small amount of invalid data is stored in the buffer. Since it is configured to be inserted, even when some data is lost due to packet loss or the like in the transmission process, a correct clock can be generated and video and audio can be reproduced with good quality.

  In another aspect of the present invention, in the above aspect of the invention, the jitter amount acquired by the jitter amount acquisition unit is converted at the same ratio as a fixed bit rate obtained by compressing the video / audio data in the transmission device. And a data amount conversion means.

  According to the aspect of the present invention, the data amount conversion unit converts the jitter amount acquired by the jitter amount acquisition unit based on the time information into a value reflecting the fixed bit rate, and uses the converted value as a buffer. Since the amount of memory used is corrected to determine the control amount of the clock generation means, an appropriate clock is generated even when video / audio data is compressed at a fixed bit rate. Can play video and audio with good quality.

  In another aspect of the present invention, in the above aspect of the present invention, the video / audio data compressed at a predetermined bit rate is transmitted at a time corresponding to the calculation result of the first difference calculation means. Data amount calculating means for calculating the amount of data to be calculated, data amount counting means for counting the data amount of the video / audio data actually transmitted while the two time information are received, and the data amount counting means Invalid data adding means for adding invalid data in an amount corresponding to the difference in the data amount to the buffer when the data amount counted in is smaller than the data amount calculated by the data amount calculating means, It further comprises invalid data deleting means for deleting the invalid data added by the invalid data adding means before the invalid data is reproduced as video / audio data. To.

  According to the aspect of the present invention, based on the received time information, the data amount of the video / audio data calculated as compressed at a predetermined bit rate is compared with the actually received data amount. When the amount of received data is small, a small amount of invalid data is inserted into the buffer. Therefore, even when video / audio data is compressed at a variable bit rate in the transmission device, the correct clock is set. Generate and play video and audio with good quality.

  According to one aspect of the present invention, the control amount correction unit subtracts the jitter amount acquired based on the time information by the jitter amount acquisition unit from the memory usage of the buffer for storing the video / audio data, and the clock generation unit. Compared to the case where the control amount of the clock generation means is simply determined based on the memory usage, the influence of jitter in the network is reduced and the quality is improved. There is an effect that video and audio can be reproduced.

  Further, according to one aspect of the present invention, the amount of data calculated from the received time information is compared with the amount of actually received data. If the amount of actually received data is small, the amount of invalidity is reduced. Since it is configured to insert data into the buffer, even if some data is lost due to packet loss in the transmission process, it is possible to generate a correct clock and reproduce video and audio with good quality There is an effect.

  Further, according to one aspect of the present invention, the data amount conversion unit converts the jitter amount acquired by the jitter amount acquisition unit based on the time information into a value reflecting the fixed bit rate, and the value after the conversion Is used to correct the memory usage of the buffer and determine the control amount of the clock generation means, so even if the video / audio data is compressed at a fixed bit rate, There is an effect that a clock can be generated and video and audio can be reproduced with good quality.

  Also, according to one aspect of the present invention, the amount of video / audio data calculated as compressed at a predetermined bit rate based on the received time information is compared with the amount of data actually received. However, when the amount of data actually received is small, a small amount of invalid data is inserted into the buffer, so even when video / audio data is compressed at a variable bit rate in the transmission device Thus, it is possible to generate a correct clock and reproduce video and audio with good quality.

  Exemplary embodiments of a receiving apparatus and a data reproducing method according to the present invention are explained in detail below with reference to the accompanying drawings. In the following embodiments, an example of a transmission device and a reception device that transmit video in real time via a network is shown, but the present invention also applies to a transmission device and a reception device that transmit audio in real time via a network. It can be applied effectively.

  First, the configuration of a conventional transmission device and reception device will be described. FIG. 11 is a block diagram showing a configuration of a conventional data transmission system. The data transmission system shown in FIG. 1 is a system for transmitting video in real time via a network 10 and includes a transmission device 100 and a reception device 200.

  The transmission device 100 is a device that converts a video signal into video data and transmits the video signal to the reception device 200 via the network 10, and includes an A / D conversion unit 111, a buffer 112, a multiplexing unit 113, and a clock reproduction unit. 114, a counter 115, and a timing generation unit 116.

  The A / D conversion unit 111 is a processing unit that changes the video signal input to the transmission device 100 to video data, and the buffer 112 temporarily stores the video data converted by the A / D conversion unit 111. It is memory. The multiplexing unit 113 is a processing unit that multiplexes the video data stored in the buffer 112 and sends the counter value stored in the counter 115 to the network 10 as time information.

  The clock recovery unit 114 is a processing unit that generates a clock for operating the transmission device 100 from the video signal input to the transmission device 100. The clock generated in the clock reproduction unit 114 is supplied to the A / D conversion unit 111 as a sampling clock for controlling the timing for sampling the video signal. The clock is also supplied to the counter 115 for counting the elapsed time, and is also supplied to the timing generation unit 116 for determining the timing for transmitting the counter value stored in the counter 115 to the receiving device 200.

  The counter 115 is a counter that increments a counter value stored by itself every time a clock is supplied from the clock reproduction unit 114, and stores an elapsed time from a certain time point as a cumulative value of the number of clocks. The timing generation unit 116 is a processing unit that notifies the multiplexing unit 113 of the timing at which the counter value stored in the counter 115 is multiplexed with video data.

  The reception device 200 is a device that converts the video data transmitted from the transmission device 100 into a video signal and outputs the video signal, and includes a separation unit 211, a D / A conversion unit 212, a counter 221, a difference calculation unit 222, VCXO (Voltage Controlled Crystal Oscillator) 223.

  The separation unit 211 is a processing unit that separates video data transmitted from the transmission device 100 and time information, and the D / A conversion unit 212 is a process that converts the video data separated by the separation unit 211 into a video signal. Part.

  Each time the clock is supplied from the VCXO 223, the counter 221 increments the counter value stored by itself. When the counter 221 receives notification that the time information is separated from the separation unit 211, the counter 221 stores the counter value stored by itself. The difference calculation unit 222 is notified.

  The difference calculation unit 222 compares the time information separated by the separation unit 211 with the counter value notified from the counter 221 to obtain a difference between the clock of the transmission device 100 and the clock of the own device, and the difference is eliminated. The control unit controls the VCXO 223 as described above.

  The VCXO 223 is a clock generation unit that can vary the frequency within a certain range, and supplies a clock for reproducing a video signal to the D / A conversion unit 212 and uses the clock for clock synchronization control. Also supplied to the counter 221.

  FIG. 12 is a diagram showing an outline of a clock correction method in the conventional data transmission system shown in FIG. As shown in the figure, the received data received by the receiving device 200 includes time data having values such as “0”, “5”, and “9” in addition to the video data converted from the video signal and the no-signal portion. Is included. These values indicate how many clocks have elapsed from a certain point in time and this time information has been transmitted.

  The difference calculation unit 222 compares the time information transmitted from the transmission device 100 with the counter value stored in the counter 221 at that time, and controls the VCXO 223 so that the difference becomes constant, thereby transmitting the difference. The clocks of the apparatus 100 and the receiving apparatus 200 are matched, and the received video can be reproduced with good quality in real time.

  However, this method assumes that the time information transmitted by the transmission device 100 is received by the reception device 200 at the same interval as that at the time of transmission, and is effective in a synchronous network where the transmission speed is stable. However, it could not be applied to an asynchronous network with a large amount of jitter such as the Internet.

  Next, a description will be given of the configuration of a transmission device and a reception device that have been conventionally used in an asynchronous network such as the Internet. FIG. 13 is a block diagram showing a configuration of another conventional data transmission system. The data transmission system shown in FIG. 1 is a system for transmitting video in real time via a network 10 and includes a transmission device 101 and a reception device 201.

  The transmission apparatus 101 is an apparatus that converts a video signal into video data and transmits the video signal to the reception apparatus 201 via the network 10. The transmission apparatus 101 includes an A / D conversion unit 111, a buffer 112, and a clock reproduction unit 114.

  The A / D conversion unit 111 is a processing unit that changes the video signal input to the transmission apparatus 101 to video data, and the buffer 112 temporarily stores the video data converted by the A / D conversion unit 111. It is memory. The clock reproduction unit 114 is a processing unit that generates a clock for operating the transmission apparatus 101 from the video signal input to the transmission apparatus 101.

  The receiving apparatus 201 includes a D / A conversion unit 212, a VCXO 223, a buffer 231, a usage status monitoring unit 232, and a PLL (Phase Locked Loop) 233. The buffer 231 is a memory that temporarily stores the video data transmitted from the transmission apparatus 101. The video data stored by itself at a rate based on the clock supplied from the VCXO 223 is D / A in a first-in first-out manner. The data is sent to the conversion unit 212.

  The usage status monitoring unit 232 monitors the amount of video data written to the buffer 231 and the amount of video data read from the buffer 231 and controls the VCXO 223 so that the amount of video data stored in the buffer 231 is constant. The PLL 233 is a circuit for suppressing variations in the control of the usage status monitoring unit 232.

  Thus, in the data transmission system shown in FIG. 13, the clock is controlled so that the memory usage of the buffer 231 is constant. Even in asynchronous networks, the amount of data transmitted over a period of a certain length is expected to be almost constant, so this method of controlling the clock based on the memory usage is used on a jittery line like the Internet. It also makes it possible to play back video with good quality in real time.

  Here, an operation example of the receiving apparatus 201 is shown. As shown in FIG. 14, when data is transmitted at equal intervals, the memory usage of the buffer 231 temporarily increases at the timing of receiving the data as shown in FIG. It will repeat the fluctuation of decreasing at.

  Since data may be written to the buffer 231 in bursts, the usage status monitoring unit 232 reads the memory usage at the timing when the data is received. That is, the usage status monitoring unit 232 reads the memory usage at each point indicated by a black circle in FIG. 15 and determines the control value of the VCXO 223. In the example of FIG. 15, the points indicated by black circles are aligned on a straight line, indicating that the control of the VCXO 223 is stable.

  FIG. 15 shows an example in which data is transmitted at an equal interval, but even when there is a slight fluctuation in the data reception interval, the VCXO 223 is controlled so that the memory usage is constant. The clock of the receiving device 201 is corrected appropriately.

  However, in an asynchronous network such as the Internet, data reception intervals may fluctuate due to communication congestion. In such a case, the quality of reproduced video is prevented from being deteriorated in such a case. I couldn't.

  For example, when there is fluctuation in data transmission as shown in FIG. 16 and the data reception interval is short, as shown in FIG. As data is received, memory usage increases. On the other hand, when the reception interval becomes longer, the read time becomes longer, and the amount of memory used cannot be increased even when the next data arrives.

  For this reason, when a large fluctuation occurs in the data reception interval, as shown in FIG. 17, the line connecting the black circles, which is the timing read by the usage status monitoring unit 232, becomes wavy, and this control is applied to the VCXO 223. Therefore, the VCXO 223 cannot perform stable clock reproduction, causing deterioration in the quality of the reproduced video.

  Next, configurations of the transmission apparatus and the reception apparatus according to the present embodiment will be described. FIG. 1 is a block diagram illustrating a configuration of a data transmission system according to the present embodiment. The data transmission system shown in FIG. 1 is a system for transmitting video in real time via a network 10 and includes a transmission device 102 and a reception device 202.

  FIG. 2 is a block diagram illustrating a configuration of the transmission apparatus 102. The transmission device 102 is a device that converts a video signal into video data and transmits the video data to the reception device 202 via the network 10, and has the same configuration as the transmission device 100. That is, the transmission device 102 multiplexes the video signal with the converted video data and transmits the time information to the reception device 202.

  FIG. 3 is a block diagram illustrating a configuration of the reception device 202. As shown in the figure, the receiving apparatus 202 includes a separation unit 211, a D / A conversion unit 212, a counter 221, a VCXO 223, a buffer 231, a usage status monitoring unit 232, a time information storage unit 241, A difference calculation unit 242, a time information storage unit 243, a difference calculation unit 244, a jitter amount acquisition unit 245, an integrator 246, and a control amount correction unit 247 are included.

  The separation unit 211 is a processing unit that separates video data transmitted from the transmission apparatus 102 and time information. The buffer 231 is a memory that temporarily stores the video data separated by the separation unit 211. The video data stored by the buffer 231 at a rate based on the clock supplied from the VCXO 223 is D / A in a first-in first-out manner. The data is sent to the conversion unit 212.

  The D / A converter 212 is a processor that converts the video data separated by the separator 211 into a video signal. The usage status monitoring unit 232 monitors the amount of video data written to the buffer 231 and the amount of video data read from the buffer 231 and controls the VCXO 223 so that the amount of video data stored in the buffer 231 is constant. It is a control part for doing.

  The VCXO 223 is a clock generation unit that can vary the frequency within a certain range, and supplies a clock for reproducing a video signal to the D / A conversion unit 212 and uses the clock for clock synchronization control. Also supplied to the counter 221.

  Each time the clock is supplied from the VCXO 223, the counter 221 increments the counter value stored by itself. When the counter 221 receives notification that the time information is separated from the separation unit 211, the counter 221 stores the counter value stored by itself. The time information storage unit 243 is notified.

  The time information storage unit 241 is a storage unit having a register 241a for storing the latest time information separated by the separation unit 211 and a register 241b for storing the previous time information, and a difference calculation unit 242. Is a processing unit for obtaining a difference between the value stored in the register 241a and the value stored in the register 241b. The calculation result of the difference calculation unit 242 represents a time difference (unit: number of clocks) at which two pieces of time information are transmitted in the transmission apparatus 102.

  The time information storage unit 243 is a storage unit having a register 243a for storing the latest counter value notified from the counter 221 and a register 243b for storing the counter value immediately before the register 243a. , A processing unit for obtaining a difference between the value stored in the register 243a and the value stored in the register 243b. The calculation result of the difference calculation unit 244 represents a time difference (unit: number of clocks) when two pieces of time information are received by the receiving device 202.

  The jitter amount acquisition unit 245 is a processing unit that determines a jitter amount in data transmission based on the calculation results of the difference calculation unit 242 and the difference calculation unit 244. The integrator 246 is a circuit that accumulates the jitter amount obtained by the jitter amount acquisition unit 245, and the control amount correction unit 247 calculates the integrator from the memory usage amount of the buffer 231 acquired by the usage state monitoring unit 232. This is a control unit that controls the correction amount of the VCXO 223 so that the value obtained by subtracting the amount of jitter accumulated in 246 becomes constant.

  Here, details of the jitter amount acquisition in the jitter amount acquisition unit 245 will be described. When the jitter amount in data transmission is 0 and the clocks of the transmission device 102 and the reception device 202 are accurately synchronized, the calculation results of the difference calculation unit 242 and the difference calculation unit 244 should match. In other words, if the calculation results of the difference calculation unit 242 and the difference calculation unit 244 do not match, either or both of the jitter amount in data transmission and the clock difference between the transmission device 102 and the reception device 202 cause a mismatch. Yes.

  Of these two factors, the difference between the clocks of the transmission device 102 and the reception device 202 is within the variable range of the VCXO 223 that generates the clock on the reception device 202 side, and therefore, the difference calculation unit 242 and the difference calculation are more than a certain value. The calculation result of the unit 244 is not affected. Therefore, as shown in FIG. 4 and FIG. 5, the jitter amount in the data transmission is a cause of mismatch in the portion where the difference between the calculation results of the difference calculation unit 242 and the difference calculation unit 244 exceeds the variable range of the VCXO 223. Can be considered.

A specific example will be described. here,
Sampling clock of transmitter 102: 27 MHz ± 0 ppm
Variable frequency of VCXO223: 27MHz ± 100ppm
It is assumed that 270000-bit video data is transmitted every 10 mS from the transmission apparatus 102 to the reception apparatus 202. It is assumed that the number of clocks counted at 27 MHz is set in the time information transmitted from the transmission device 102 to the reception device 202.

  In this case, the length of each clock generated by the VCXO 223 is about 37 nS, and a variation of about ± 2.7 clocks per 1 mS can be considered. That is, when the difference between the calculation results of the difference calculation unit 242 and the difference calculation unit 244 is ± 2.7 clocks or more per 1 mS, at least that portion can be regarded as being due to line jitter.

Therefore, when the difference between the calculation results of the difference calculation unit 242 and the difference calculation unit 244 is (A), the jitter component in the number of clocks per 1 mS is obtained as follows.
(A) ≧ 3: (A) -3
When (A) ≦ 3: (A) +3
When the absolute value of (A) <3: 0
Note that “3” above is obtained by replacing 2.7 with an integer that is a large value that satisfies the condition.

  The jitter amount acquisition unit 245 acquires the jitter amount by converting the jitter component at the predetermined number of clocks per time thus obtained into a data amount. Usually, since 1-bit video data is transmitted per clock, a value obtained by excluding the variable value of the VCXO 223 from the difference between the calculation results of the difference calculation unit 242 and the difference calculation unit 244 becomes the jitter amount as it is.

  As described above, the receiving apparatus 202 according to the present embodiment controls the jitter amount acquired by the jitter amount acquisition unit 245 based on the time information from the memory usage amount of the buffer 231 acquired by the usage status monitoring unit 232. Since the amount correction unit 247 is configured to subtract and determine the control amount of the VCXO 223, the influence of jitter in the network is reduced compared with the case where the control amount of the VCXO 223 is simply determined based on the memory usage. Video can be reproduced with good quality.

  In the method of correcting the clock on the receiving side based on the memory usage, the clock may be disturbed not only by line jitter but also by packet loss due to a failure or the like. This is because the amount of memory used is reduced from the original amount due to packet loss. In this embodiment, a configuration for preventing clock disturbance due to packet loss is shown.

  FIG. 6 is a block diagram illustrating the configuration of the receiving device 203 according to the present embodiment. Similar to the reception device 202, the reception device 203 is a device that receives the video data transmitted from the transmission device 102, converts it into a video signal, and outputs the video signal. As shown in the figure, in addition to the configuration of the receiving device 202 shown in FIG. 3, the receiving device 203 includes a data amount calculation unit 251, a data amount counting unit 252, an invalid data insertion unit 253, and invalid data deletion. Part 254.

  The data amount calculation unit 251 calculates the amount of video data that should be received while the two pieces of time information stored in the time information storage unit 241 are received based on the calculation result of the difference calculation unit 242. The data amount counting unit 252 is a processing unit that counts the amount of video data actually received during that time.

  The invalid data insertion unit 253 compares the data amount calculated by the data amount calculation unit 251 with the data amount counted by the data amount counting unit 252, and the data amount counted by the data amount counting unit 252 is greater. This is a processing unit that adds invalid data corresponding to the difference between the two to the normal video data and inserts it into the buffer 231 when the number is small.

  Thus, the invalid data insertion unit 253 inserts invalid data into the buffer 231, so that the amount of data lost due to packet loss is supplemented, and the VCXO 223 can be appropriately controlled. The invalid data deletion unit 254 is a processing unit that deletes invalid data inserted by the invalid data insertion unit 253 at a stage before conversion by the D / A conversion unit 212.

  The invalid data inserted into the buffer 231 by the invalid data insertion unit 253 is provided with a special flag or given a specific bit pattern so that it can be distinguished from normal video data. .

  As described above, the receiving device 203 according to the present embodiment compares the data amount calculated from the received time information with the actually received data amount, and when the actually received data amount is small, Since a small amount of invalid data is inserted into the buffer 231, a correct clock can be generated even when some data is lost due to packet loss in the transmission process.

  In the above example, the example of the simplest control is shown. However, the data amount calculated in the data amount calculation unit 251 and the data amount count so as not to accidentally insert invalid data into the buffer 231. When the difference in the amount of data counted in the unit 252 is smaller than the packet size, control such as suppression of invalid data insertion may be added.

  In this embodiment, a case where video data is compressed and transmitted will be described. When video data is compressed and transmitted, the amount of memory used will be less than it should be in the same way as when packet loss occurs. I can't. The present embodiment shows a configuration for solving this problem.

  FIG. 7 is a block diagram illustrating the configuration of the data transmission system according to the present embodiment. The data transmission system shown in FIG. 1 is a system for transmitting video in real time via the network 10 and includes a transmission device 104 and a reception device 204. The transmission device 104 converts the input video signal into video data, compresses the video data, and transmits the compressed video signal to the reception device 204. Then, the receiving device 204 expands the compressed video data, converts it into a video signal, and outputs it.

  FIG. 8 is a block diagram illustrating the configuration of the transmission apparatus 104 according to the present embodiment. As shown in the figure, the transmission apparatus 104 includes an encoding unit 117 in addition to the configuration of the transmission apparatus 102 shown in FIG. The encoding unit 117 is a processing unit that compresses the video data converted by the A / D conversion unit 111 by encoding and outputs the compressed video data to the buffer 112. Here, it is assumed that the encoding unit 117 compresses video data at a fixed bit rate.

  FIG. 9 is a block diagram illustrating a configuration of the receiving device 204 according to the present embodiment. As shown in the figure, in addition to the configuration of the receiving device 202 shown in FIG. 3, the receiving device 204 includes a data amount calculation unit 251, a data amount counting unit 252, an invalid data insertion unit 253, and invalid data deletion. A unit 254, a data amount conversion unit 261, a carryover amount storage unit 262, a frequency dividing circuit 263, and a decoding unit 264.

  The data amount calculation unit 251 calculates the amount of video data that should be received while the two pieces of time information stored in the time information storage unit 241 are received based on the calculation result of the difference calculation unit 242. The data amount counting unit 252 is a processing unit that counts the amount of video data actually received during that time.

  Note that the data amount calculation unit 251 calculates the data amount in consideration of a fixed bit rate at which the video data is compressed. For example, when the video data is compressed to 1/10, the data amount calculation unit 251 sends a value obtained by reducing the data amount calculated from the calculation result of the difference calculation unit 242 to 1/10 to the invalid data insertion unit 253. .

  The invalid data insertion unit 253 compares the data amount calculated by the data amount calculation unit 251 with the data amount counted by the data amount counting unit 252, and the data amount counted by the data amount counting unit 252 is greater. This is a processing unit that adds invalid data corresponding to the difference between the two to the normal video data and inserts it into the buffer 231 when the number is small.

  Here, the data amount counted by the data amount counting unit 252 is the actually transmitted compressed data amount, and the data amount calculated by the data amount calculating unit 251 is calculated by reflecting the fixed bit rate. Therefore, the amount of invalid data inserted into the buffer 231 reflects the fixed bit rate.

  The invalid data deletion unit 254 is a processing unit that deletes invalid data inserted by the invalid data insertion unit 253 at a stage prior to decoding by the decoding unit 264. Note that the data amount calculation unit 251, the data amount counting unit 252, the invalid data insertion unit 253, and the invalid data deletion unit 254 according to the present embodiment are portions necessary for processing for complementing the data amount lost due to packet loss or the like. Yes, it is not an essential part when video data is compressed and transmitted.

  The data amount conversion unit 261 is a processing unit that converts the jitter amount acquired by the jitter amount acquisition unit 245 into a value that reflects the fixed bit rate, and the carry amount storage unit 262 is the data amount conversion unit 261. It is a storage unit that stores fractions generated in conversion and reflects them in the next conversion.

  The frequency dividing circuit 263 is a circuit that converts the clock generated in the VCXO 223 into a clock for reading video data compressed at a fixed bit rate. For example, when the video data is compressed to 1/10, the frequency dividing circuit 263 divides the clock generated in the VCXO 223 by 1/10.

  The reason for dividing the clock in this way is that the data stored in the buffer 231 is reduced by the compression. The decryption unit 264 is a processing unit that decompresses the video data after the invalid data is deleted by the invalid data deletion unit 254 and decompresses the video data, and outputs the video data to the D / A conversion unit 212.

Here, the clock correction processing in the receiving apparatus 204 will be described with a specific example. here,
Sampling clock of transmitter 104: 27 MHz ± 0 ppm
Variable frequency of VCXO223: 27MHz ± 100ppm
Fixed bit rate of encoding: 1/10
It is assumed that 27000-bit data obtained by compressing 270000-bit video data every 10 mS is transmitted from the transmission device 104 to the reception device 204. It is assumed that the number of clocks counted at 27 MHz is set in the time information transmitted from the transmission device 104 to the reception device 204.

  If the transmission apparatus 104 transmits time information at 10 mS intervals under the above conditions, the calculation result of the difference calculation unit 242 is 270000. At this time, if the calculation result of the difference calculation unit 244 is 275400, the difference between the calculation results of the difference calculation unit 242 and the difference calculation unit 244 is 5400, and the variation amount per 10 mS of the VCXO 223 is ± 27 clocks. Therefore, the output of the jitter amount acquisition unit 245 is 5373.

  Since the fixed bit rate of encoding is 1/10, the output of the data amount conversion unit 261 is 537, 0.3 after the decimal point is stored in the carry amount storage unit 262, and the next data amount This is reflected in the calculation result of the conversion unit 261.

  As described above, in the receiving apparatus 204 according to the present embodiment, the data amount conversion unit 261 converts the jitter amount acquired by the jitter amount acquisition unit 245 based on the time information into a value reflecting the fixed bit rate. Since the control amount of the VCXO 223 is determined by correcting the memory usage of the buffer 231 using the value after conversion, even when the video data is compressed at a fixed bit rate. Proper clock can be generated and good quality video can be played.

  In the third embodiment, the case where video data is compressed at a fixed bit rate has been described, but in this embodiment, the case where video data is compressed at a variable bit rate will be described.

  FIG. 10 is a block diagram illustrating the configuration of the receiving device 205 according to the present embodiment. As shown in the figure, in addition to the configuration of the receiving device 202 shown in FIG. 3, the receiving device 205 includes a data amount calculation unit 251, a data amount counting unit 252, an invalid data insertion unit 253, and invalid data deletion. Unit 254 and decoding unit 264.

  The data amount calculation unit 251 calculates the amount of video data that should be received while the two pieces of time information stored in the time information storage unit 241 are received based on the calculation result of the difference calculation unit 242. The data amount counting unit 252 is a processing unit that counts the amount of video data actually received during that time. Note that the data amount calculation unit 251 calculates the data amount without considering the bit rate at which the video data is compressed.

  The invalid data insertion unit 253 compares the data amount calculated by the data amount calculation unit 251 with the data amount counted by the data amount counting unit 252, and the data amount counted by the data amount counting unit 252 is greater. This is a processing unit that adds invalid data corresponding to the difference between the two to the normal video data and inserts it into the buffer 231 when the number is small.

  Here, since the data amount calculated in the data amount calculation unit 251 is calculated without reflecting the bit rate, the memory usage of the buffer 231 after the invalid data is inserted is the video data. This is the same amount of memory used when not compressed. Therefore, the buffer 231 always stores the amount of data that should be stored when the video data is not compressed, and the receiving device 205 is involved in the bit rate for compressing the video data on the transmission side. Therefore, it is possible to always generate an appropriate clock and reproduce a video of good quality.

  In the above example, an example in which the same amount of data as in the case where video data is not compressed is always accumulated in the buffer 231 is shown. May be stored in the buffer 231. Further, the configuration of the receiving apparatus 205 according to the present embodiment is effective not only when the video data is compressed at a variable bit rate but also when the bit rate at which the video data is compressed is unknown.

  In each of the above embodiments, the transmitting device and the receiving device are shown as devices having different configurations. However, the transmitting device and the receiving device may be combined to function as both a transmitting device and a receiving device. It is also possible to realize a device that can.

(Supplementary Note 1) A receiver that reproduces video / audio data transmitted from a transmitter via a network in real time,
Clock generation means for generating a clock for reproducing the video / audio data;
A buffer for temporarily storing the video / audio data;
First difference calculation means for calculating a time difference between two pieces of time information transmitted from the transmission device multiplexed with the video / audio data, thereby obtaining a time difference between the two pieces of time information transmitted in the transmission device; ,
A second difference calculating means for calculating a time difference between a time when one of the two time information arrives at the receiving device and a time when the other arrives at the receiving device;
Occurs due to fluctuations in the clock generated by the clock generation means from the data amount of the video / audio data transmitted at a time corresponding to the difference between the calculation results of the first difference calculation means and the second difference calculation means. A jitter amount acquisition means for acquiring a jitter amount in the network by subtracting a possible data fluctuation amount;
A control amount correction unit that corrects a control amount applied to the clock generation unit so that a value obtained by subtracting the jitter amount acquired by the jitter amount acquisition unit from the data amount stored in the buffer is constant. A receiving apparatus.

(Supplementary Note 2) Data amount calculation means for calculating the data amount of the video / audio data to be transmitted at a time corresponding to the calculation result of the first difference calculation means;
A data amount counting means for counting a data amount of the video / audio data actually transmitted while the two pieces of time information are received;
Invalid data for adding invalid data in an amount corresponding to the difference in data amount to the buffer when the data amount counted by the data amount counting unit is smaller than the data amount calculated by the data amount calculating unit Additional means,
The receiving apparatus according to claim 1, further comprising invalid data deleting means for deleting the invalid data added by the invalid data adding means before the invalid data is reproduced as video / audio data.

(Additional remark 3) It further has the data amount conversion means which converts the jitter amount acquired by the said jitter amount acquisition means by the same ratio as the fixed bit rate which compressed the said video / audio data in the said transmitter. The receiving apparatus according to Supplementary Note 1 or 2.

(Supplementary Note 4) Data amount calculating means for calculating the amount of data to which the video / audio data compressed at a predetermined bit rate should be transmitted at a time corresponding to the calculation result of the first difference calculating means;
A data amount counting means for counting a data amount of the video / audio data actually transmitted while the two pieces of time information are received;
Invalid data for adding invalid data in an amount corresponding to the difference in data amount to the buffer when the data amount counted by the data amount counting unit is smaller than the data amount calculated by the data amount calculating unit Additional means,
The receiving apparatus according to claim 1, further comprising invalid data deleting means for deleting the invalid data added by the invalid data adding means before the invalid data is reproduced as video / audio data.

(Supplementary Note 5) A data reproduction method in a receiving apparatus for reproducing video / audio data transmitted from a transmitting apparatus via a network in real time,
An accumulation step of temporarily accumulating the video / audio data in a buffer;
A first difference calculating step of calculating a time difference between the two pieces of time information transmitted from the transmission device by multiplexing with the video / audio data, thereby obtaining a time difference between the two pieces of time information transmitted in the transmission device; ,
A second difference calculating step of calculating a time difference between a time when one of the two time information arrives at the receiving device and a time when the other arrives at the receiving device;
Generated to reproduce the video / audio data from the data amount of the video / audio data transmitted at a time corresponding to the difference between the calculation results of the first difference calculation step and the second difference calculation step. A jitter amount acquisition step of acquiring a jitter amount in the network by subtracting a data fluctuation amount that may occur due to clock fluctuations;
A control amount correction step of correcting a control amount for changing the clock so that a value obtained by subtracting the jitter amount acquired by the jitter amount acquisition step from the data amount stored in the buffer is constant. A data reproduction method characterized by that.

(Appendix 6) A data amount calculation step of calculating a data amount of the video / audio data to be transmitted at a time corresponding to a calculation result of the first difference calculation step;
A data amount counting step of counting a data amount of the video / audio data actually transmitted while the two pieces of time information are received;
Invalid data for adding invalid data in an amount corresponding to the difference in data amount to the buffer when the data amount counted in the data amount counting step is smaller than the data amount calculated in the data amount calculating step Additional steps;
The data reproduction method according to claim 5, further comprising: an invalid data deletion step of deleting invalid data added by the invalid data addition step before the invalid data is reproduced as video / audio data. .

(Supplementary note 7) The method further includes a data amount conversion step of converting the jitter amount acquired in the jitter amount acquisition step at the same ratio as a fixed bit rate obtained by compressing the video / audio data in the transmission device. The data reproduction method according to appendix 5 or 6,

(Supplementary note 8) A data amount calculation step of calculating a data amount to which the video / audio data compressed at a predetermined bit rate should be transmitted at a time corresponding to the calculation result of the first difference calculation step;
A data amount counting step of counting a data amount of the video / audio data actually transmitted while the two pieces of time information are received;
Invalid data for adding invalid data in an amount corresponding to the difference in data amount to the buffer when the data amount counted in the data amount counting step is smaller than the data amount calculated in the data amount calculating step Additional steps;
The data reproduction method according to claim 5, further comprising an invalid data deletion step of deleting invalid data added by the invalid data addition step before the invalid data is reproduced as video / audio data. .

  As described above, the receiving apparatus and the data reproducing method according to the present invention are useful when reproducing video / audio data transmitted from a transmitting apparatus via a network in real time, and in particular, the influence of jitter in network transmission. This is suitable when it is necessary to reproduce video and audio with good quality.

It is a block diagram which shows the structure of a data transmission system. It is a block diagram which shows the structure of a transmitter. It is a block diagram which shows the structure of a receiver. It is a figure which shows the outline | summary of the clock correction method. It is a figure which shows the outline | summary of the clock correction method. It is a block diagram which shows the structure of a receiver. It is a block diagram which shows the structure of a data transmission system. It is a block diagram which shows the structure of a transmitter. It is a block diagram which shows the structure of a receiver. It is a block diagram which shows the structure of a receiver. It is a block diagram which shows the structure of the conventional data transmission system. It is a figure which shows the outline | summary of the clock correction method. It is a block diagram which shows the structure of another conventional data transmission system. It is a figure which shows the case where data are transmitted equally. It is a figure which shows the state of the buffer when data are transmitted equally. It is a figure which shows the case where there is fluctuation in data transmission. It is a figure which shows the state of a buffer when there is fluctuation in data transmission.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Network 100-102,104 Transmission apparatus 111 A / D conversion part 112 Buffer 113 Multiplexing part 114 Clock reproduction part 115 Counter 116 Timing generation part 117 Encoding part 200-205 Reception apparatus 211 Separation part 212 D / A conversion part 221 Counter 222 Difference calculation unit 223 VCXO
231 Buffer 232 Usage monitoring unit 233 PLL
241, 243 Time information storage unit 241a, 241b, 243a, 243b Register 242, 244 Difference calculation unit 245 Jitter amount acquisition unit 246 Integrator 247 Control amount correction unit 251 Data amount calculation unit 252 Data amount counting unit 253 Invalid data insertion unit 254 Invalid data deletion unit 261 Data amount conversion unit 262 Carry-over amount storage unit 263 Frequency divider 264 Decoding unit

Claims (5)

A receiving device that reproduces video / audio data transmitted from a transmitting device via a network in real time,
Clock generation means for generating a clock for reproducing the video / audio data;
A buffer for temporarily storing the video / audio data;
First difference calculation means for calculating a time difference between two pieces of time information transmitted from the transmission device multiplexed with the video / audio data, thereby obtaining a time difference between the two pieces of time information transmitted in the transmission device; ,
A second difference calculating means for calculating a time difference between a time when one of the two time information arrives at the receiving device and a time when the other arrives at the receiving device;
Occurs due to fluctuations in the clock generated by the clock generation means from the data amount of the video / audio data transmitted at a time corresponding to the difference between the calculation results of the first difference calculation means and the second difference calculation means. A jitter amount acquisition means for acquiring a jitter amount in the network by subtracting a possible data fluctuation amount;
A control amount correction unit that corrects a control amount applied to the clock generation unit so that a value obtained by subtracting the jitter amount acquired by the jitter amount acquisition unit from the data amount stored in the buffer is constant. A receiving apparatus. A data amount calculating means for calculating a data amount of the video / audio data to be transmitted at a time corresponding to a calculation result of the first difference calculating means;
A data amount counting means for counting a data amount of the video / audio data actually transmitted while the two pieces of time information are received;
Invalid data for adding invalid data in an amount corresponding to the difference in data amount to the buffer when the data amount counted by the data amount counting unit is smaller than the data amount calculated by the data amount calculating unit Additional means,
2. The receiving apparatus according to claim 1, further comprising: invalid data deleting means for deleting the invalid data added by the invalid data adding means before the invalid data is reproduced as video / audio data. .   2. The data amount conversion means for converting the jitter amount acquired by the jitter amount acquisition means at the same ratio as a fixed bit rate obtained by compressing the video / audio data in the transmission device. Or the receiving apparatus of 2. A data amount calculating means for calculating a data amount to which the video / audio data compressed at a predetermined bit rate should be transmitted at a time corresponding to a calculation result of the first difference calculating means;
A data amount counting means for counting a data amount of the video / audio data actually transmitted while the two pieces of time information are received;
Invalid data for adding invalid data in an amount corresponding to the difference in data amount to the buffer when the data amount counted by the data amount counting unit is smaller than the data amount calculated by the data amount calculating unit Additional means,
2. The receiving apparatus according to claim 1, further comprising: invalid data deleting means for deleting the invalid data added by the invalid data adding means before the invalid data is reproduced as video / audio data. . A data reproducing method in a receiving apparatus for reproducing video / audio data transmitted from a transmitting apparatus via a network in real time,
An accumulation step of temporarily accumulating the video / audio data in a buffer;
A first difference calculating step of calculating a time difference between the two pieces of time information transmitted from the transmission device by multiplexing with the video / audio data, thereby obtaining a time difference between the two pieces of time information transmitted in the transmission device; ,
A second difference calculating step of calculating a time difference between a time when one of the two time information arrives at the receiving device and a time when the other arrives at the receiving device;
Generated to reproduce the video / audio data from the data amount of the video / audio data transmitted at a time corresponding to the difference between the calculation results of the first difference calculation step and the second difference calculation step. A jitter amount acquisition step of acquiring a jitter amount in the network by subtracting a data fluctuation amount that may occur due to clock fluctuations;
A control amount correction step of correcting a control amount for changing the clock so that a value obtained by subtracting the jitter amount acquired by the jitter amount acquisition step from the data amount stored in the buffer is constant. A data reproduction method characterized by that.

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